The present invention relates to an optical disk player and a method of controlling an optical disk player, more precisely relates to an optical disk player and a method of controlling an optical disk player, in each of which rotational speed of an optical disk, e.g., CD-R/RW, DVD-R/RW, can be properly changed on the basis of a shape of the optical disk.
Many types of optical disk players, in each of which a circular optical disk or disks are attached, are known (see Japanese Patent Gazette No. 11-66712, etc.). Recently, noncircular optical disks (see FIGS. 5 and 6) are used.
The noncircular optical disk 30 shown in FIG. 5 is made by merely cutting a circular optical disk. Data can be written in a whole face 30a of the disk 30. But, a part 30b is actually used as an effective recording part because data can be continuously written in and read from the part 30b. 
The noncircular disk 40 shown in FIG. 6 is made by covering one side face of a circular optical disk 50, e.g., 8 cm circular disk, with a rectangular cover 40a, whose width is slightly greater than a diameter of the circular disk 50. Letters and characters can be written on a rear face of the cover 40a. For example, the noncircular optical disk 40 can be used as a business card. Data can be written in an exposed whole face 40b of the disk 50.
Data can be written in and read from the noncircular optical disks by conventional optical disk players.
However, conventional optical disk players rotate optical disks at high speed, e.g., 24× speed or more. Some optical disk players have 48× speed.
When data are written in or read from the noncircular optical disk at such high speed, a linear edge of the noncircular disk collides with air stream caused by the high speed rotation of the optical disk. As the result of the collision, a lifting force works to the noncircular disk, so that the noncircular disk greatly vibrates and occurs loud noise. Further, data cannot be written and read stably. In the worst case, the optical disk player is broken by the vibration.
If the rotational speed of the optical disk player is fixed at lower speed so as to stably use a noncircular disk, it takes a long time to write data in and read data from a circular disk too.